FrançaisWhat Giardia is and which dogs carry it
Giardia duodenalis lives in the small intestine. It releases cysts in the stool, which are infective right away, can survive for months in the environment, and only a few are needed to infect another dog [1, 2]. Cysts appear in the stool 4 to 16 days after infection, and shedding usually lasts several weeks to months [1].
It is common. A worldwide review found a pooled prevalence of 15.2% in dogs, much higher in young dogs [4]. In Europe the overall figure is around 3–7%, but higher in dogs under one year of age [1]. In 29 French breeding kennels, 41% of puppies aged 5 to 14 weeks tested positive [8]. In the Netherlands, 64.9% of hunting dogs living in groups were positive, against 7.9% of household dogs [5].
Signs and what the stool looks like
- Most infections are silent: many dogs shed cysts without any signs [1, 2].
- Diarrhea that can be acute, intermittent or chronic, sometimes with gas, vomiting or weight loss [2].
- Typical stool: soft, poorly formed, pale, foul-smelling, with mucus and a fatty look. Watery diarrhea is unusual and blood is usually absent [3].
- Dogs most at risk of signs: puppies after weaning or rehoming, stressed dogs, and dogs with other infections or a weak immune system [1].
Diarrhea in puppies has many causes, including parvovirus, coccidia and hookworms.
How Giardia is found: the stool tests
| Test | What it detects | Key points |
|---|---|---|
| Zinc sulfate centrifugal flotation | Cysts under the microscope | Preferred flotation solution; sugar solutions distort cysts [2]. Sensitivity 86% in one study of young dogs [6]. |
| Fecal antigen (ELISA, rapid SNAP-type test) | Giardia proteins in the stool | Can be positive when cysts are temporarily absent [1]. Rapid test sensitivity 74–91% depending on the study, specificity 96% or higher [6, 9]. |
| Immunofluorescence (IFA/DFA) | Cysts stained with a fluorescent antibody | Used in laboratories, often as the reference test [6, 7]. |
| PCR | Giardia DNA | Very sensitive (97% in one study) but less specific [5]; mainly useful to identify the assemblage [3, 6]. |
Because cysts are shed on and off, one negative sample does not rule Giardia out. Guidelines suggest three samples over 3–5 days, or repeated testing on alternating days [1, 2, 3].
In dogs with long-standing silent infection, in-house tests had good negative but poor positive predictive values at the prevalences common in practice [7]. For dogs with diarrhea, CAPC recommends combining a direct smear, a centrifugal flotation and a sensitive fecal antigen test or PCR [2].
Reading a Giardia result line
Stool test results are not numbers. Here is an illustrative line from a fecal antigen test.
- Abbreviation The name varies by laboratory: Giardia Ag, Giardia ELISA or SNAP Giardia for the rapid in-clinic test.
- Result Positive means Giardia antigen was found in this sample. It shows infection, not necessarily disease [1].
- Unit No unit: the result is positive or negative. Some flotation reports give a number of cysts.
- Laboratory interval Negative is the expected result. A negative sample does not rule out infection because shedding is intermittent [2].
- Flag No H or L flag for this kind of result. Antigen and PCR can stay positive for a while after treatment, so they are not used to judge treatment success [2].
What the blood work shows
Giardia stays in the gut and the routine laboratory findings are usually normal [3]. Blood work does not diagnose Giardia. Vets may still run a blood count and chemistry in a dog with chronic diarrhea or weight loss, to look for other causes or for effects such as low protein.
A positive dog without signs, retesting and people
- Dogs with diarrhea that test positive should be treated, according to ESCCAP and CAPC [1, 2].
- Positive dogs without signs: ESCCAP does not generally advise treatment, but a risk assessment: treatment is advised in kennels with diarrhea in puppies, with small children or immunocompromised people, or when a zoonotic strain is found [1]. CAPC’s majority opinion is that dogs without signs may not need treatment [2].
- Retesting: ESCCAP suggests a control sample within 3 days of the last treatment, to tell a persistent infection from a new one [1]. CAPC suggests a zinc sulfate flotation 24–48 hours after treatment if signs have not resolved [2]. Reinfection from the environment is common [1, 2].
- Risk for people: dogs mostly carry dog-type assemblages C and D, while people are almost always infected with A or B [1]. In Sardinia, 49% of typed dog samples were D, 36.1% C and 4.2% A2 [11]. In Spanish households, no dog-to-owner transmission was found [10]. Transmission appears rare, but vulnerable people should limit exposure and wash their hands [2].
Related articles
See also eosinophils in dogs and cats, sometimes raised with parasites. En français : giardiose du chien.
Questions to ask your veterinarian
- Which test was used: flotation, antigen test, immunofluorescence or PCR?
- Should we test more samples over the next few days?
- My dog has no signs: is treatment needed in our situation?
- When and with which test should we recheck after treatment?
- Should the assemblage be checked because someone at home is vulnerable?
Get your dog’s test results explained together.
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Frequently asked questions
How long does it take for Giardia to leave a dog?
Without treatment, shedding usually lasts several weeks to months, and many dogs carry it without signs. Reinfection from the environment is common, so it can seem to last longer [1, 2].
Can I cuddle my dog with Giardia?
Dogs mostly carry dog-type strains, and transmission to people appears rare [1, 2]. Good hygiene still matters: wash your hands, pick up stool, and people with a weak immune system should limit close contact [2].
What would Giardia poop look like?
Usually soft, poorly formed, pale and foul-smelling, with mucus and a fatty look. Watery diarrhea is unusual and blood is usually absent [3].
Sources
- ESCCAP. Guideline 06: Control of Intestinal Protozoa in Dogs and Cats, 3rd edition, March 2025. esccap.org/guidelines/gl6
- Companion Animal Parasite Council (CAPC). Giardia (dog). Updated August 2026. capcvet.org/guidelines/giardia
- Robertson LJ. Giardiasis in Animals. Merck Veterinary Manual. Updated May 2026. merckvetmanual.com/digestive-system/giardiasis-giardia/giardiasis-in-animals
- Bouzid M et al. The prevalence of Giardia infection in dogs and cats, a systematic review and meta-analysis of prevalence studies from stool samples. Vet Parasitol. 2015;207(3-4):181-202. doi.org/10.1016/j.vetpar.2014.12.011
- Uiterwijk M et al. Comparing four diagnostic tests for Giardia duodenalis in dogs using latent class analysis. Parasit Vectors. 2018;11(1):439. doi.org/10.1186/s13071-018-3014-2
- Uehlinger FD et al. Comparison of five diagnostic tests for Giardia duodenalis in fecal samples from young dogs. Vet Parasitol. 2017;244:91-96. doi.org/10.1016/j.vetpar.2017.07.030
- Rishniw M et al. Comparison of 4 Giardia diagnostic tests in diagnosis of naturally acquired canine chronic subclinical giardiasis. J Vet Intern Med. 2010;24(2):293-7. doi.org/10.1111/j.1939-1676.2010.0475.x
- Grellet A et al. Risk factors of weaning diarrhea in puppies housed in breeding kennels. Prev Vet Med. 2014;117(1):260-5. doi.org/10.1016/j.prevetmed.2014.07.016
- Kanski S et al. Performance of the Vetscan Imagyst in point-of-care detection of Giardia duodenalis in canine fecal samples. J Vet Diagn Invest. 2025;37(1):63-70. doi.org/10.1177/10406387241279177
- de Lucio A et al. No molecular epidemiological evidence supporting household transmission of zoonotic Giardia duodenalis and Cryptosporidium spp. from pet dogs and cats in the province of Álava, Northern Spain. Acta Trop. 2017;170:48-56. doi.org/10.1016/j.actatropica.2017.02.024
- Pipia AP et al. Canine giardiosis in Sardinia Island, Italy: prevalence, molecular characterization, and risk factors. J Infect Dev Ctries. 2014;8(5):655-60. doi.org/10.3855/jidc.4255
Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.